netdev - Re: [PATCH v2] 802.11n IBSS: wlan0 stops receiving packets due to aggregation after sender reboot

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Message-ID: <8c4325e2-6ec6-59f1-89df-36392f674530@ncentric.com>
Date:   Tue, 29 Oct 2019 10:40:07 +0100
From:   Koen Vandeputte <koen.vandeputte@...ntric.com>
To:     Sebastian Gottschall <s.gottschall@...media-net.de>,
        Johannes Berg <johannes@...solutions.net>,
        Krzysztof Hałasa <khalasa@...p.pl>
Cc:     "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] 802.11n IBSS: wlan0 stops receiving packets due to
 aggregation after sender reboot


On 29.10.19 09:58, Sebastian Gottschall wrote:
> 35 km? for 802.11n with ht40 this is out of the ack timing range the 
> chipset supports. so this should be considered at any troubles with 
> connections
>
(Please don't top-post)

When we know a link can exceed ~ 21km, it's set to HT20 for this reason.

Koen

> Am 29.10.2019 um 09:41 schrieb Koen Vandeputte:
>>
>> On 28.10.19 13:21, Johannes Berg wrote:
>>> On Fri, 2019-10-25 at 12:21 +0200, Krzysztof Hałasa wrote:
>>>> Fix a bug where the mac80211 RX aggregation code sets a new 
>>>> aggregation
>>>> "session" at the remote station's request, but the head_seq_num
>>>> (the sequence number the receiver expects to receive) isn't reset.
>>>>
>>>> Spotted on a pair of AR9580 in IBSS mode.
>>>>
>>>> Signed-off-by: Krzysztof Halasa <khalasa@...p.pl>
>>>>
>>>> diff --git a/net/mac80211/agg-rx.c b/net/mac80211/agg-rx.c
>>>> index 4d1c335e06e5..67733bd61297 100644
>>>> --- a/net/mac80211/agg-rx.c
>>>> +++ b/net/mac80211/agg-rx.c
>>>> @@ -354,10 +354,13 @@ void ___ieee80211_start_rx_ba_session(struct 
>>>> sta_info *sta,
>>>>                */
>>>>               rcu_read_lock();
>>>>               tid_rx = rcu_dereference(sta->ampdu_mlme.tid_rx[tid]);
>>>> -            if (tid_rx && tid_rx->timeout == timeout)
>>>> +            if (tid_rx && tid_rx->timeout == timeout) {
>>>> +                tid_rx->ssn = start_seq_num;
>>>> +                tid_rx->head_seq_num = start_seq_num;
>>>>                   status = WLAN_STATUS_SUCCESS;
>>> This is wrong, this is the case of *updating an existing session*, we
>>> must not reset the head SN then.
>>>
>>> I think you just got very lucky (or unlucky) to have the same dialog
>>> token, because we start from 0 - maybe we should initialize it to a
>>> random value to flush out such issues.
>>>
>>> Really what I think probably happened is that one of your stations lost
>>> the connection to the other, and didn't tell it about it in any way 
>>> - so
>>> the other kept all the status alive.
>>>
>>> I suspect to make all this work well we need to not only have the fixes
>>> I made recently to actually send and parse deauth frames, but also to
>>> even send an auth and reset the state when we receive that, so if we
>>> move out of range and even the deauth frame is lost, we can still reset
>>> properly.
>>>
>>> In any case, this is not the right approach - we need to handle the
>>> "lost connection" case better I suspect, but since you don't say what
>>> really happened I don't really know that that's what you're seeing.
>>>
>>> johannes
>>
>> Hi all,
>>
>> I can confirm the issue as I'm also seeing this sometimes in the 
>> field here.
>>
>> Sometimes when a devices goes out of range and then re-enters,
>> the link refuses to "come up", as in rx looks to be "stuck" without 
>> any reports in system log or locking issues (lockdep enabled)
>>
>> I have dozens of devices installed offshore (802.11n based), both on 
>> static and moving assets,
>> which cover from short (250m) up to very long distances (~35km)
>>
>> So .. while there is some momentum for this issue,
>> I'm more than happy to provide extensive testing should fixes be 
>> posted regarding IBSS in general.
>>
>> Regards,
>>
>> Koen
>>
>>